Calculation the Critical Clearing Time CCT for Iraqi super grid in a fast manner of three - phase fault

Abstract

This paper describes the use of direct method (Relative Unstable Equilibrium Point method (RUEP)) to evaluate the Critical Clearing Time (CCT) of power system subjected to large contingencies. The main aim is to reduce the execution time of the process of finding of the Critical Clearing Time for transient stability analysis, this method runs fast but with poor accuracy due to the over-simplification of component models; the time-domain simulation method is accurate but time- consuming. Results of the (RUEP) method applied on the simulation examples and actual system calculation are analyzed, and the range of error is discussed. Via complementarity of direct method and time-domain simulation method, a new crossbred method is proposed: in the calculation of the critical clearing time, the result of the direct method is used as the initial value and then the time-domain simulation method is employed for further search, which can meet the requirements of transient stability in terms of accuracy and speed. The results obtained by two methods show that the proposed method reduces the execution time of the Central Processing Unit about 8-10 times. In this paper the CCT was calculated for power system 400kvIraq Super Grid.